Abstract:
Sclerotinia sclerotiorum, a homothallic plant pathogen, undergoes sexual reproduction via haploid selfing (equivalent to clonal
reproduction), and produces long-lasting surviving vegetative structures called sclerotia, enhancing clonal persistence and
spread. Thus it is not surprising to detect clones of the species. Whether outcrossing can occur in the homothallic S. sclerotiorum
remains unanswered. Early studies showed that S. sclerotiorum has a clonal population structure, consistent with its life history
traits. However, recent studies using polymorphic and co-dominant molecular markers showed frequent genetic recombination,
suggesting outcrossing. This review focuses on recent developments in population genetics studies related to detecting recombination,
random association of alleles and dynamic mating type (MAT) alleles in Sclerotinia. Despite frequent reports of random
association of alleles, the mechanisms for outcrossing in a homothallic species remain elusive. Recent intriguing findings are: the
MAT genes in Sclerotinia are subject to inversion or deletion in every meiotic generation, the MAT gene deletion is related to
ascospore dimorphism and mating type switching in S. trifoliorum, and ascospore dimorphism was also observed in S.
sclerotiorum. Determining the nature of the dimorphic ascospores and their prevalence in relation to environmental cues could
significantly advance our understanding how S. sclerotiorum populations behave in nature
